Dynamoelectric machines such as electric motors typically include a stator assembly having one or more windings, a rotor assembly rotatably mounted within the stator assembly, and a shell or housing surrounding the stator assembly. Energy losses sustained by a motor in converting electrical energy to mechanical power arise chiefly through the electrical and magnetic characteristics of the motor. For example, since the rotor of a motor is subjected to time-varying magnetic flux, eddy currents will be induced in it thereby causing some energy loss. To minimize this eddy-current loss, rotors typically are built up of thin members or laminations which are stacked together in what is known as "skewed" relation.
More specifically, rotor laminations are typically planar disc shaped members formed by a stamping operation. A typical rotor lamination includes a central opening and at least one skew pin hole located radially outwardly from the central opening. Each lamination is identical to the other laminations forming a particular rotor, and a predetermined number of laminations of known thickness can be stacked to form a rotor of a desired height or length. The laminations are stacked with the center openings thereof concentric. To provide the "skewed" relation between the laminations, the laminations are rotated relative to one another about their common central axis such that the skew pin holes of successive laminations are progressively angularly offset from the skew pin hole of the first lamination. The angle of rotation between the skew pin hole of the last or top lamination and that of the first or bottom lamination is known as the "skew angle".
The laminations can be assembled into a stack for making a rotor using a wide variety of assembly techniques, for example, utilizing a four station assembly process. In this example, a first work station is provided for stacking the laminations to a desired height. A second work station is provided for measuring the height of the lamination stack to ensure that the proper number of laminations have been stacked at the first station. A third work station is provided for setting the skew angle and welding the laminations together. A fourth work station is provided for unloading the welded laminations. The four work stations are located at spaced locations adjacent the periphery of a rotatable table. The table is provided with tooling or fixturing at spaced work locations or positions around a central axis of rotation of the table such that when one work location is positioned, for instance, at the first work station for stacking the laminations, a second work location is positioned at the second station for measuring.
Tooling or fixturing at each work location can include means forming a planar surface for receiving and locating the first lamination, a central mandrel, and an adjustable skewing pin. The central mandrel is typically fixed in position in an upward orientation perpendicular to the planar locating surface. The skew pin also extends upwardly but is mounted so that it may be angularly rotated relative to the central mandrel by moving a skew pin angle setting arm relative to the central mandrel.
To stack the laminations on the work location, the central opening of a lamination is aligned with the central mandrel and the skew pin hole is aligned with the top of the skew pin. The lamination is then slid down the central mandrel and skew pin to a position on the planar surface of the work location or on top of the previously loaded lamination. As discussed above, laminations are loaded in this manner until the desired stack height is attained.
When the skew pin is angularly rotated relative to the central mandrel, the stacked laminations also are rotated about the mandrel such that the respective skew pin holes of the laminations are offset from one another. That is, although the central openings of the stacked lamination are axially aligned, the axes of the skew pin holes are angularly offset from one another, and the skew pin hole of the topmost lamination will be offset from the bottom lamination by the desired skew angle.
To set up the four work locations in the above example, skew pin adjustments must be made for each of the locations. Particularly, each skew pin at each work location must be set to be disposed at the same skew angle to enable accurate assembly of the rotors. In the past, given the desired skew angle and lamination stack height, an operator first calculated the angular orientation of the skew pin. The operator then set the skew pin angle at each work location utilizing a protractor to visually align the skew pin for that work location to the desired setting.
Calculating the skew pin angle and setting the skew pin at four work locations is a time consuming process. In addition, since such setting requires an operator to visually set the skew pin angle utilizing a protractor, such setting is susceptible to operator error. An operator must be extremely careful to ensure that the skew pin angle is set to precisely the same angle at each location. Moreover, the operator must make separate calculations for each different combination of stack height and skew angle used to make different rotors. Making such calculations and setting the pin skew angles using a protractor for visual alignment certainly is less than desirable, particularly due to the time and operator skill required.
Accordingly,it is desirable and advantageous to provide a method and apparatus which greatly simplifies the process of setting the skew pin angle by eliminating the need for an operator to make mathematical calculations. It also is desirable and advantageous to provide a method and apparatus which does not require reading a protractor or other instrument in setting the skew angle.
An object of the present invention is to provide a skew pin angle setting method and apparatus which enables an operator to simply locate the skew pin to a predetermined alignment position to set a desired skew angle.
Another object of the present invention is to provide a skew pin angle setting method and apparatus which reduces the amount of time required to set the skew pin angle.
Yet another object of the present invention is to provide a skew pin angle setting method and apparatus which reduces the possibility for operator error and improves consistency in making skew pin angle settings at a number of work locations.
Still another object of the present invention is to provide a skew pin angle setting method and apparatus which eliminates any need for an operator to make mathematical calculations in determining the setting for a skew pin.